iOS学习 - 20 UICollectionView 移动 Item ，类似背包

//UICollectionViewDataSource
- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath*)destinationIndexPath;

#pragma mark -- 手势开始
- (void)xwp_gestureBegan:(UILongPressGestureRecognizer *)longPressGesture{
    CGFloat y = [longPressGesture locationInView:longPressGesture.view].y;
    //超过数据源的 item 不执行
    if (y <= [self row]) {
        //获取手指所在的cell
        _originalIndexPath = [self indexPathForItemAtPoint:[longPressGesture locationOfTouch:0 inView:longPressGesture.view]];
        UICollectionViewCell *cell = [self cellForItemAtIndexPath:_originalIndexPath];
        //使用系统自带方法截图
        UIView *tempMoveCell = [cell snapshotViewAfterScreenUpdates:NO];
        //隐藏当前 Item
        cell.hidden = YES;
        _tempMoveCell = tempMoveCell;
        _tempMoveCell.frame = cell.frame;
        [self addSubview:_tempMoveCell];
        
        //开启边缘滚动定时器
        [self xwp_setEdgeTimer];
        //开启抖动
        if (_shakeWhenMoveing && !_editing) {
            [self xwp_shakeAllCell];
            [self addObserver:self forKeyPath:@"contentOffset" options:NSKeyValueObservingOptionNew context:nil];
        }
        _lastPoint = [longPressGesture locationOfTouch:0 inView:longPressGesture.view];
        //通知代理
        if ([self.delegate respondsToSelector:@selector(dragCellCollectionView:cellWillBeginMoveAtIndexPath:)]) {
            [self.delegate dragCellCollectionView:self cellWillBeginMoveAtIndexPath:_originalIndexPath];
        }
    }
}

#pragma mark -- 手势抖动
- (void)xwp_gestureChange:(UILongPressGestureRecognizer *)longPressGesture{
    //获取点击位置 y 值
    CGFloat y = [longPressGesture locationInView:longPressGesture.view].y;
    //限制手势范围 y 值
    if (y <= [self row]) {
        NSLog(@"-----%f",y);
        //通知代理
        if ([self.delegate respondsToSelector:@selector(dragCellCollectionViewCellisMoving:)]) {
            [self.delegate dragCellCollectionViewCellisMoving:self];
        }
        CGFloat tranX = [longPressGesture locationOfTouch:0 inView:longPressGesture.view].x - _lastPoint.x;
        CGFloat tranY = [longPressGesture locationOfTouch:0 inView:longPressGesture.view].y - _lastPoint.y;
        _tempMoveCell.center = CGPointApplyAffineTransform(_tempMoveCell.center, CGAffineTransformMakeTranslation(tranX, tranY));
        _lastPoint = [longPressGesture locationOfTouch:0 inView:longPressGesture.view];
        [self xwp_moveCell];
    }else{
        //如果超过范围，就把当前拖动的 item y 值设为数据源的底部
        _tempMoveCell.frame = CGRectMake(_tempMoveCell.frame.origin.x, [self row], _tempMoveCell.frame.size.width, _tempMoveCell.frame.size.height);
    }
}

#pragma mark -- 手势取消或者结束
- (void)xwp_gestureEndOrCancle:(UILongPressGestureRecognizer *)longPressGesture{
    UICollectionViewCell *cell = [self cellForItemAtIndexPath:_originalIndexPath];
    self.userInteractionEnabled = NO;
    [self xwp_stopEdgeTimer];
    //通知代理
    if ([self.delegate respondsToSelector:@selector(dragCellCollectionViewCellEndMoving:)]) {
        [self.delegate dragCellCollectionViewCellEndMoving:self];
    }
    //一个小动画
    [UIView animateWithDuration:0.25 animations:^{
        _tempMoveCell.center = cell.center;
    } completion:^(BOOL finished) {
        [self xwp_stopShakeAllCell];
        [_tempMoveCell removeFromSuperview];
        cell.hidden = NO;
        self.userInteractionEnabled = YES;
    }];
}